In order to increase recording density of a hard disk drive (HDD), the miniaturization of the dimension of a magnetic head has been progressing year after year. FIG. 2 illustrates an external view of an HDD. An enclosure includes a magnetic disk 3, a head gimbal assembly (HGA) 4, and a voice coil motor 6 that performs positioning drive of the HGA 4, and the magnetic head is included in a head slider 7 installed at the proximal end part of the HGA 4. The magnetic disk 3 is rotationally driven by a motor. The magnetic head is positioned at a desired track of the magnetic disk by driving the HGA 4 by the voice coil motor 6. As a magnetic head, an induced type head that serves as both of a recording head and a read head has been used in the past, however, the current mainstream is a write/read-separated head that separates a recording head and a reproduction head for improving the performance. The recording head is an inductive head to write information using induced magnetic field by a coil, and the read head is a Giant Magneto-Resistance (GMR) head or a Tunnel Magneto-Resistance (TMR) head using a spin valve as a magnetic sensor.
FIG. 3 illustrates a schematic diagram of a write/read-separated type head that includes a recording head unit 1 and a read head unit 2. A surface viewed from “A” in FIG. 3 corresponds to an air bearing surface (ABS), which faces a magnetic disk, of a head slider. FIG. 4 illustrates an enlarged view around a main pole 8 of the recording head unit 1. The recording head is constituted by the main pole 8, a trailing shield 9, and a side shield 10 when viewed from the ABS surface. The integration of the trailing shield 9 and the side shield 10 is also referred to as a wrap around shield (WAS).
In order to continuously improve the recording density, for a magnetic head, various new technologies have been proposed. Here, two types of new technologies related to the present invention are described. First, a shingled write magnetic recording system for narrowing a recording width (track pitch) on a magnetic disk is described. FIG. 5 is a principle illustrative diagram of the shingled write system. In a conventional recording system, a track pitch is matched with a magnetic recording width by main pole magnetic field, and on the other hand, in the shingled write system, a track pitch is set to become narrower than a magnetic recording width, so that the recording is performed so as to be overwritten on some tracks. Therefore, the scanning direction of the track is limited, for example, to one direction indicated by an arrow 12 of FIG. 5. However, the width of a recording mark 13 can be set to become narrower than the width of the main pole 8, thereby performing recording with high density. In a product of an existing perpendicular magnetic recording technology, the recording density has reached the level of 500 Gb/in2, and, from the fact that there is limitation around 1 Tb/in2, a technology for enhancing the recording density to the improved level of 1 to 2 Tb/in2 has been reviewed. A state in which overwriting is performed in sequence is reminiscent of roof tiles, so that the word of “shingled (tiled)” is used.
In the shape of the recording head for the shingled write system, there is no need to narrow the track width, and with the aim of increasing the magnetic field gradient of a direction across the track (cross-track direction) and obtaining sufficient magnetic field strength in order to sharply perform different writing between tracks, as illustrated in FIG. 6, a structure of the recording head has been proposed in which the narrow side shield 10 is provided only on one side, and as the dimension of the main pole 8, for example, the track width is set as 50 to 150 nm so as to be relatively large. The main point of this technology is to increase the magnetic field gradient on the side used for writing and increase the track pitch, and the design is optimized for the main point. The actual width of a recorded track is set to become narrower than the width of the magnetic pole within a range that takes into account an obtained magnetic field gradient.
Next, a microwave-assisted magnetic recording (MAMR) system is described as another new technology. As discussed in Non Patent literature 1, the MAMR system is a system in which precession of magnetization of a medium is caused by using high-frequency magnetic field by a microwave generation layer and the reversal of magnetization is assisted so as to be easily caused by magnetic field from the main pole. When magnetic anisotropy energy of the medium is increased for high density, the reversal of magnetization is difficult to be caused only by the magnetic field from the main pole, so that such an assisted recording system is desired.
FIG. 7 illustrates a schematic diagram of an MAMR head viewed from a surface (slider side surface) that is perpendicular to an ABS surface and parallel to the central line of the main pole. The MAMR head generates a spin-polarized current in a magnetic layer of a spin injection layer 20 that flows a current from the main pole and is arranged adjacent to the main pole 8, injects the spin-polarized current into a microwave generation layer (field generation layer=FGL) 19, causes oscillation by utilizing spin torque, and generates electromagnetic waves (microwaves) having high-frequency. The microwave is irradiated to a medium 3, locally induces precession of the magnetization, and assists the magnetization reversal by recording head magnetic field. An auxiliary layer 18, etc. are provided adjacently to the FGL layer depending on a configuration. A microwave generation current 21 from the main pole is flowed toward the trailing shield 9.